For some time automotive manufacturers have been aware that the application of disc or drum brakes to slow or stop a vehicle may cause a significant amount of noise to emanate from the vehicle. It has been learned that such noise originates at the interface of a brake drum and a friction material brake block or at the interface of a rotor and the friction material of a disc brake pad during the braking application. During such application a resonance develops at the friction material brake drum or rotor interface which may be transmitted through the brake shoe assembly, the brake mounting hardware and into the suspension to cause objectionable noise to emanate from the vehicle.
Numerous attempts have been made to reduce the resonance vibration imparted during the braking operations. In vehicles equipped with disc brakes in which a disc brake pad engages a rotor, resonant vibrations have been reduced by providing a resilient coating at the interface between a disc brake pad backing plate and a caliper piston. Unfortunately, a conventional drum brake mechanism does not lend itself to such a solution. In an attempt to reduce the aforementioned resonant vibrations it has been the practice to stiffen certain brake and suspension system components to reduce their susceptibility to developing sympathetic resonant vibrations. Attempts to stiffen such systems have included casting ribs on the exterior surface of a brake drum to stiffen the drum, casting brake drums with a heavy ring of metal around the edge of the open end of the drum to stiffen the drum and welding supports on the suspension system to more firmly anchor suspension components to reduce their ability to transmit and/or amplify vibrations. Additionally, heavy rubber bands sometimes are secured to the exterior surface of brake drums in an attempt to reduce the vibrations transmitted therethrough. Unfortunately, none of the aforementioned mentions provide a definitive solution to the problem applicable to all vehicles.
Large vehicles such as trucks and busses are particularly susceptible to the generation of excessive noise during the braking process and the aforementioned attempts to reduce the resonance emanating from the brake drum friction material interface have been least successful in these applications.
Accordingly, it is desirable to provide an automotive brake shoe assembly which is capable of interrupting and reducing the noise carrying vibrations originating at the friction material/brake drum interface during the braking application. It has been found desirable to interrupt these noise transmitting vibrations as close to this interface as possible.